It should be noted that reference to the prior art herein is not to be taken as an acknowledgement that such prior art constitutes common general knowledge in the art.
Where high fidelity reproduction of sound is required, many requirements must be met. The most basic of these requirements is that the loudspeaker must be designed to reproduce all of the human audible frequency range. Therefore, a loudspeaker is an electroacoustic transducer which converts an electrical audio signal into a corresponding sound. A loudspeaker for the audiophile or home user will typically include an enclosure in which speaker drivers and associated electronic hardware, such as crossover circuits, are mounted. The simplest of enclosures are designed from rectangular particle-board boxes. The very complex loudspeaker cabinets can incorporate composite materials, internal baffles, horns, ports and acoustic insulation.
The enclosure housing provides a resonance space. One of the fundamental requirements for designing a loudspeaker is to achieve a low resonant frequency in a speaker enclosure that has a relatively small internal volume and this comes at a compromise. With the loudspeaker transducer mounted within an enclosure or box the ability to reproduce sound is dependent on the interaction of the motion of the transducer to the acoustic behaviour of the enclosure.
Sealed loudspeaker design has always been difficult due to the reduction in low frequency efficiency of the transducer when placed in an enclosure. This inefficiency, coupled with the large enclosure needed to match the performance of a typical modestly sized ported design has resulted in sealed designs being relatively rare and in particular in the audiophile and home user market. However, one advantage of using a sealed design is the accurate time-domain step response and a far gentler low frequency (LF) roll-off. Using a sealed enclosure also provides a usable output which extends to a much lower frequency.
The use of professional sound reinforcement drivers (PA Drivers) was designed to reinforce sound to make it louder or distribute it to a wider audience. Therefore, professional sound reinforcement (PA) drivers are defined as drivers designed for large scale and large area applications including performance halls, cinemas, clubs, concerts, places of worship and outdoor venues. A PA bass driver or woofer when compared with its Hi-Fi equivalent is physically much larger in size. Professional sound reinforcement drivers designed for low frequency bass reproduction to the lowest octave of the audible spectrum are 15, 18 and 21 inches in diameter and almost always employ a surround that is of the accordion type giving rigidity. These drivers also have a large power handling and lower compliance suspension system (in comparison to Hi Fi speakers) with the resonant frequency (Fs) of the driver being higher as a compromise. Therefore for these drivers to operate effectively requires either very large enclosures and/or ported enclosure designs.
Where high fidelity reproduction of sound is required, multiple loudspeaker transducers are often mounted in the same enclosure, each reproducing a part of the audible frequency range.
Clearly it would be advantageous if a sealed loudspeaker and loudspeaker driver could be devised that helped to at least ameliorate some of the shortcomings described above. In particular, it would be beneficial to provide a sealed loudspeaker, loudspeaker driver and design process for producing loudspeakers and drivers which utilised professional sound reinforcement (PA) drivers to produce a loudspeaker which was suitable for the audiophile and home environment.